Excimer lamp with high pressure fill

ABSTRACT

An excimer lamp utilizing a high pressure fill. The fill includes a halogen at an operating pressure of greater than about 350 torr or the combination of a halogen and a rare gas at a total operating pressure of greater than about 2.5 atmospheres.

The present application is a continuation of U.S. application Ser. No.08/008,783, filed Jan. 27, 1993, now U.S. Pat. No. 5,504,391, which is acontinuation-in-part of U.S. application Ser. No. 07/999,580, nowabandoned, filed Dec. 29, 1992, which is a continuation of U.S.application Ser. No. 07/827,041, now abandoned, filed Jan. 29, 1992.U.S. application Ser. No. 08/008,783 is incorporated herein byreference.

The present invention is directed to an improved excimer lamp.

In recent years, many industrial processes have been developed which useultraviolet radiation to treat material. In some such processes, thematerial has a photocurable coating thereon, and the ultravioletradiation "cures" the coating by a chemical reaction. Such photocurablecoatings may for example be clear or pigmented, and are applied to avariety of objects including flat substrates and curved objects such ascans. Photocurable coatings are also used in practicing semiconductorphotolithography, which is a process which is used in the manufacture ofintegrated circuits.

The ultraviolet lamp which is used to irradiate photocurable coatingstypically utilizes a bulb fill which contains mercury, with an additiveor additives sometimes being present to add emphasis to a particularregion or regions of the spectrum. Thus, the spectrum of the light whichis emitted by the lamp is the spectrum of the element mercury, or thatof mercury plus a particular additive.

The spectrum of mercury as generated by such lamps has radiation presentthroughout the fairly broad spectral band of 200-400 nanometers. Sincethe radiation is distributed throughout the entire band, the efficiencyof the lamp in any particular narrower part of the entire band isrelatively low.

For some applications, it would be desirable to have most of theradiation output of the lamp within a narrower band. By way of example,some photocurable materials are much more responsive to ultravioletradiation within the relatively narrow 250-300 nanometer band than toradiation in other parts of the ultraviolet spectrum. Such a materialwould be more rapidly cured by a lamp which has most of its outputconcentrated within the 250-300 nanometer band.

In recent years, discharge devices which emit excimer radiation havebecome known. Excimers are unstable excited complexes of molecules thatunder normal conditions possess an unbound or weakly bound ground state,and thus are not known from classical physics. That is, the excimercomplexes exist only in the excited state. The excimer complexesdisintegrate within less than a microsecond, and during their decay giveoff their binding energy in the form of radiation in a narrow band.

While the most common excimer devices are lasers, recently a microwavepowered excimer lamp has been disclosed. In the article entitled "NewHigh-Efficiency Quasi-Continuous Operation of A KrF (B→X) Excimer LampExcited by Microwave Discharge" by Kumagai and Obara, Applied Physicsletters, Vol. 54, No. 26, Jun. 26, 1989, pp. 2619-2621, a lamp whichemits radiation in a very narrow band of several nanometers about 248 nmis discussed. The lamp utilizes a fill having small amounts of fluorineand krypton in a buffer gas mixture of helium and neon. The articleteaches that it is required to operate the lamp at a low pressure toachieve suitable efficiency, with an efficiency of 12.1% being attainedat a desired total pressure of 50 torr and a halogen pressure of 1 torr.This efficiency may not be high enough for certain applications.

In accordance with a broadest aspect of the present invention, anexcimer lamp is provided which contains a fill which includes a halogenat a pressure which is greater than about 350 torr at operatingtemperature. In accordance with the invention, even better results areobtained when the halogen pressure is greater than about 750 torr duringoperation, and still better results are obtained when the halogenpressure is greater than about 6 atmospheres. The fill may contain ahalogen or a halogen and a rare gas.

In accordance with a further aspect of the invention, an excimer lamp isprovided which contains a fill which includes a rare gas and a halogen,wherein the total fill pressure is greater than about 2.5 atmospheres atoperating temperature, and preferably above 10 atmospheres. Inaccordance with this aspect of the invention, the partial pressure ofthe halogen may be greater or less than 350 torr.

It is noted that substances may be added to the fill to provide spectralemphasis. For example zinc may be included in an excimer containing fillto add spectral emphasis in the 250-350 nanometer range. Furthermore,the fill may contain combinations of halogens, the combination of a raregas and multiple halogens, multiple rare gas/halogen combinations, or ahalogen and multiple rare gases. Alternatively, the fill may consistonly of a halogen, or the combination of a halogen and a rare gas.

In accordance with the microwave excited embodiment of the invention,microwave energy is provided by a magnetron or other device, while thefill is contained in a suitable envelope, such as one which is made ofquartz. The microwave energy is coupled to the fill by a coupling meanswhich includes a mesh which is opaque to the microwave energy, butsubstantially transparent to the excimer radiation which is emitted bythe fill, to enable the radiation to be directed out of the lamp.

The invention will be better understood by referring to the accompanyingdrawings wherein:

FIG. 1 is a representation of the spectrum between 200 and 400 nm whichis provided by a microwave lamp having a mercury fill.

FIGS. 2 to 5 show an embodiment of the present invention which utilizesa linear bulb.

FIG. 6 is a representation of the spectral output of a lamp inaccordance with an embodiment of the invention.

FIG. 7 is a representation of the spectral output of a lamp inaccordance with another embodiment of the invention.

FIG. 8 shows a further embodiment of the invention, which utilizes aspherical bulb.

FIGS. 9 and 10 show still further embodiments of the invention.

Referring to FIG. 1, the ultraviolet spectrum which is generated by amicrowave powered lamp having a mercury fill is depicted. As may beseen, the ultraviolet power output of the lamp is distributed throughoutthe 200-400 nanometer range. As discussed above, it may be desirable tohave the power concentrated in a narrower range, for if a particularphotocurable substance only responds within such a narrow range, theremainder of the power is largely wasted.

A lamp in accordance with a first embodiment of the present invention isdepicted in FIGS. 2 to 5. The lamp is seen to include envelope or bulb 4which contains the excimer forming fill, magnetron 20, and couplingmeans for coupling the microwave energy which is generated by magnetron20 to the bulb fill.

The coupling means includes microwave cavity 2 which is comprised ofreflector 6 and mesh 8. As is seen in FIG. 2, the reflector 6 includesslots 16 and 18, through which microwave energy is coupled.Additionally, mesh 8 is substantially opaque to the microwave energy soas to contain it in the cavity, while being substantially transparent tothe radiation which is emitted by the fill in bulb 4.

A further part of the microwave coupling means in the particular lampillustrated in FIGS. 1 to 4 is metallic, inverted box structure 22.Referring to FIGS. 2, 4, and 5, it will be seen that the structure iscomprised of sidewall member 48, and angularly disposed members 50 and52. Structure 22 fits over reflector 6 as illustrated in FIGS. 2 and 5,and the structure in combination with the reflector forms a microwaveenclosure or waveguide means for transferring microwave energy to thecoupling slots. The magnetron launcher is disposed in opening 24 whichis located equidistant from the chamber ends, and the launcher is thuslocated in the waveguide means equidistant from the coupling slots. Thebottom of inverted box-like structure 22 has flanges 24 and 26 which maybe secured to cooperating flanges 28 and 30 which extend from thereflector, for example by being screwed thereto.

Structure 22 may additionally have members 32 and 34 shown in FIG. 5running along the length of the inside of sidewalls 40 and 42 andconnecting these sidewalls to the reflector. Members 32 and 34 have theeffect of shortening the height of the waveguide means, and providingfor more efficient coupling of the microwave energy to slots 16 and 18.Additionally, the sidewalls of the waveguide means have cooling holes 54therein and reflector 6 has cooling holes 56 along the top, as shown inFIG. 3. The lamp is cooled by pushing or pulling air or other coolinggas through the waveguide means and microwave chamber past the lampenvelope.

The frequency of the microwave energy generated by magnetron 20 and thelongitudinal dimension of chamber 2 are arranged so that duringoperation a symmetrical standing wave exists in the microwave chamberwhich has a minimum or null at the middle of the chamber in thelongitudinal direction. When so energized, the microwave couplingstructure illustrated in FIGS. 1 to 4 couples microwave energy toenvelope 4 in such manner that the envelope produces a balanced outputacross its length.

In accordance with a first and broadest aspect of the invention, thefill in bulb 4 includes a halogen, or the combination of a halogen and arare gas, wherein the halogen is at a pressure of greater than about 350torr at operating temperature. As mentioned above, better results areobtained when the halogen pressure is greater than about 750 torr, andstill better results are obtained when the halogen pressure duringoperation is greater than about 6 atmospheres

In accordance with a further aspect of the invention, in a bulb whichcontains a fill which includes the combination of a rare gas and ahalogen, the total fill pressure is arranged to be greater than about2.5 atmospheres at operating temperature, and preferably above 10atmospheres, while the halogen pressure may be greater or less than 350torr.

Ten rare gas/halogen combinations emit excimer radiation, and these areXeBr, KrBr, XeI, XeCl, KrCl, ArCl, XeF, KrF, ArF, and NeF. Additionally,the fill may include multiple halogens and a rare gas, multiple raregases and a halogen, or multiple halogens and multiple rare gases.Additionally, it may be desirable to add substances to the fill toprovide spectral emphasis in different regions of the spectrum. Forexample, mercury, zinc, cadmium, or some combination of them may be usedas additives for this purpose.

When a lamp such as is shown in FIGS. 2 to 5 utilizes a high pressurefill in accordance with the invention as described above, excimerradiation at suitable efficiency is emitted. The radiation is reflectedby reflector 6 through mesh 8 to the exterior of the lamp, where theradiation is utilized. Furthermore, in implementations which were built,it was found that within certain limits efficiency increased with fillpressure, and again within certain limits that efficiency increased withpower density. The power density is arranged to be in excess of about225 watts/cc, and preferably in excess of about 1000 watt/cc, which withsuitable cooling results in an operating temperature (wall temperature)of between about 750° C. and 950°.

In a particular lamp similar to the one depicted in FIGS. 2 to 5, a fillcontaining a mixture of xenon and bromine was utilized. The bromine waspresent at a pressure of about 7.2 atmospheres while the xenon waspresent at about 2.5 atmospheres at operating temperature. The powerinput to the lamp was 1482 watts.

The spectrum which was provided by this lamp is shown in FIG. 6. It isseen that most of the radiation is concentrated over a range of about 50nanometers (250-300 nm), in distinction to the spectrum of the mercurylamp which is shown in FIG. 1. The spectrum includes a XeBr line whichis followed by a Br₂ line, and it should be noted that the visiblespectrum (above 400 nm) is flat and without structure. It was found thatthe efficiency of the lamp tended to increase with increasing fillpressure.

In another case, the bulb was again filled with xenon and bromine, withthe bromine pressure being about 7.2 atmospheres and the xenon pressurebeing about 5 atmospheres during operation. A power of 1168 watts wasapplied to the lamp, and the spectrum shown in FIG. 7 resulted. Theefficiency of the lamp was 14.6% in the 250-300 nanometer range, whichis a higher efficiency than that disclosed in the prior art Kumagai andObara lamp discussed above.

It should be noted that the spectra illustrated in FIGS. 6 and 7 havemost of the radiation concentrated in a band of about 50 nanometers,which is a substantially broader band than in the embodiments disclosedin Kumagai and Obara. This is an important advantage for certainapplications. It also should be appreciated that different specificfills can result in spectra wherein the radiation is concentrated inbands of different widths.

The procedure which was used for filling the above bulbs was to fill amanifold with a fixed pressure of liquid bromine and xenon, then usingliquid nitrogen, freeze out most of the contents of the manifold into asingle bulb. The nubbin was added to the end of the bulb while itscontents were frozen. Of course the halogen may be added to the bulb bythe use of a halide compound. The procedure to start the lamps was tospray liquid nitrogen onto the bulbs to freeze the bromine, whereupon aTesla coil was placed near the bulb while under microwave-excitation tostart the lamp.

Referring to FIG. 8, a further embodiment of the invention whichutilizes a microwave lamp which incorporates a spherical bulb isdepicted. In this embodiment, bulb 70 is disposed in a microwave cavitywhich is comprised of reflector 72 and mesh 74. Magnetron 76 providesmicrowave energy, which is fed by waveguide 78 through the slot 80 inreflector 72. The ultraviolet radiation which is emitted by bulb 70 isreflected by reflector 72 through mesh 74, so as to exit the lamp. Thebulb is cooled by being rotated by motor 82 while pressurized air isdirected to the bulb. The lamp which is depicted in FIG. 8 may use abulb fill as heretofore described to produce excimer radiation.

While the preferred embodiment of the fill of the present invention isin connection with a microwave powered lamp, the fill may be used toprovide excimer radiation in any type of electrically excited lamp,including R.F. powered lamps and arc lamps.

In this regard, FIG. 9 depicts electrodeless lamp 100, having a fill asdescribed above, which is powered by R.F. energy. Referring to theFigure, R.F. oscillator 102 provides electromagnetic energy in the R.F.range which is fed to coil 104, which is arranged to inductively couplesthe energy to lamp 100 at a suitably high power density. As is known tothose skilled in the art, capacitive coupling may be used in lieu ofinductive coupling.

FIG. 10 depicts an arc lamp 110 having electrodes 112 and 114, which isprovided with the fill of the present invention. Arc lamp power supply112 couples electrical energy to the lamp, so as to provide excimerradiation.

An improved lamp for providing excimer radiation has thus beendisclosed. It should be appreciated that while the invention has beendisclosed in connection with illustrative embodiments, variations willoccur to those skilled in the art, and the scope of the invention is tobe limited only by the claims appended hereto as well as equivalents.

We claim:
 1. A microwave powered electrodeless lamp,comprising,microwave energy generating means, a microwave cavity, anenvelope containing substance which emits excimer radiation uponexcitation disposed in said microwave cavity, said substance comprisinghalogen in an amount sufficient to result in a halogen pressure ofgreater than about 350 torr at operating temperature, and means forcoupling microwave energy produced by said microwave energy generatingmeans to said cavity to cause said substance to emit excimer radiation.2. The lamp of claim 1 wherein said substance which emits excimerradiation consists essentially of halogen.
 3. The lamp of claim 1wherein said substance which emits excimer radiation consistsessentially of halogen and rare gas.
 4. The lamp of claims 2 or 3wherein the amount of halogen is such to result in a halogen pressure ofgreater than about 750 torr at operating temperature.
 5. The lamp ofclaims 2 or 3 wherein the amount of halogen is such to result in ahalogen pressure of greater than about 6 atmospheres at operatingtemperature.
 6. The lamp of claim 5 wherein said halogen is chlorine. 7.The lamp of claim 3 wherein said halogen is bromine and said rare gas isxenon.
 8. An electrodeless lamp bulb, comprising,an envelope which doesnot include exterior electrodes thereon, and substance in said envelopewhich emits excimer radiation when excited, said substance consistingessentially of halogen in an amount sufficient to result in a halogenpressure of greater than about 350 torr at operating temperature.
 9. Anelectrodeless lamp bulb, comprising,an envelope which does not includeexterior electrodes thereon, and substance in said envelope which emitsexcimer radiation when excited, said substance consisting essentially ofrare gas and halogen wherein the halogen is present in an amountsufficient to result in a halogen pressure of greater than about 350torr at operating temperature.
 10. The bulb of claim 8 or 9 wherein thehalogen is present in an amount sufficient to result in a halogenpressure of greater than about 6 atmospheres at operating temperature.